Sound recording and reproducing unit



April 25, 1.933- J. M. KENISALL 1,905,175

SOUND RECORDING AND REPRODUCING UNIT Filed March 12, 1931 '2 Sheets-Sheet l v e James 776. liendall,

I QWE Q April 25, 1933. J. M. KENDALL 1,905,175-

SOUND RECORDING AND REPRODUCING UNIT I Filed March 12, 1931 Sheets-Shee't 2 .Eendall,

o l N m Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE;

JAMES M. KENDALL, 0F WOODBI'J'RY HEIGHTS, NEW JERSEY, ASSIGNOB, BY MESNE ASSIGNMENTS, TO RADIO CORPORATION OF AMERICA, 01 NEW YORK, N. Y.,-A COR- PORATION OF DELAWARE SOUND RECORDING AND REPRODUCING UNI'I' Application filed larch '12, 1981.

My invention relates to sound recording and reproducing apparatus, and it has particular relation to apparatus of the type adapted to employ wax or other suitable sound record tablets or disks having a mechanical sound track in a surface thereof.

More specifically, my inventionrelates to that'unita'ry portion of asound recording and reproducing apparatus of the above type which operates directly in connection with the record tablet or disk to finally record in, or initially reproduce sounds from, the groove or sound track. This unitary portion of the apparatus, which may be termed the sound recording and reproducing unit, includes 'a suitable device for translating vibratory or electrical impulses into a corresponding motion of a stylus with which the device is provided, for recordingin the sound track or record groove, or for translating motion of the stylus derived from the'sound track or record groove into correspondiiig vibratory sound or electrical impulses.

The translating device is carried in operative relation to the record disk whereby the stylus is permitted-to follow the sound track, by a suitable supporting means or suspension arm which is pivotally mounted to permit the translating device to be movablefreely both in a plane parallel with and also in a direction perpendicular to the surface of the record disk in which the soundtrack is located. The suspension arm is, of necessity, elongated axially whereby it supports the translating device over the active portion of the record surface from a fixed point of support. v With sound translating units heretofore known, difliculty has been experiencedv in' eliminating the distorting effect upon the sound translation of vibrational forces acting upon the translating device.

I have found that distorting influences upon the sound translation may often be 'caused by communication of the vibrations of the stylus to the translating device itself and to the/suspension means, and the reflection of these vibrations back to the stylus.

The reflected vibrations, like others when in phase with those of the stylus, tend to augment, and when out of phase therewith Serial No. 521,936.

tend to diminish, the amplitude of its vibrations, thereby varying the character of the signal being translated, from that desired and intended.

By an analysis of the above andother similar objectionable influences I have found-that a major portion of the vibrations are torsional vibrations of the translating device and suspension means or arm, the vibrations occurring about the axis of the suspension arm or an axis approximately determined by and extending through the center of mass of the translating device itself and the pivotal con- .nection of the arm with its supporting pedestal.

I have found that an undesirable torsional resonance causing vibration, common to many types of suspension arms, occurs within a range of substantially 90 to 150 cycles.

Resonance is also encountered to some extent, at frequencles above this range. Resonance within this range is particularly troublesome may be impressed upon the stylus through the suspension means.

Because of these influences, in operation, the recording stylus may frequently be dislodged from one turn of the sound track or groove to another, being advanced or retracted in its course and thus skipping a portion of the record or being caused to repeat a portion already transcribed. Thisdifliculty occurs particularly with vibrations of low frequency and great amplitude.

From the foregoing it will be seen that the translating device may be subjected to vibratory influences from the stylus and the associated ap aratus, or either of them, the ex ternal v1 ratory forces I being transmitted from the fixed point of sup rt through the sus nsion means, while vi ration from the 5 sty us is received "directly. .It will be understood that, when the stylus is .enga ed with the record track or groove, the a ove .described resonant or other undesired vibratory movement of the translating device tends to cause undesired relative movement between the stylus and said device,-,thereby introducing distortion into the recording or reproduc tion of the sounds. It is, therefore, a primary object of my invention to provide an improved sound record- I ing and reproducing unlt, including a soundtranslating device and a suitable sup rt therefor, which obviates'the above described and similar difiiculties heretofore experienced with units of that character and which is simple in construction and adapted for manufacture at low cost. 1 v

More specifically, it is an object of my invention to provide a sound recording'and re 25 producing unit, including a translating de-' vice and a support. therefor, of such construction that the translating device will not partake of, or be influenced to vibrate, by the vibrations of the stylus bar or of the associated cabinet or other supporting structure of the apparatus. y

In carryin out my invention, I provide an 1 improved unit that is so constructed and the parts are so arranged that the eifect'of vibrations from sources external to the unit and the vibrationalinfluences generated in the unit, as for example, by the stylus, are. re vented from afl'ecting the recording an reproduc' action of the translating device and causing distortion: of the reporded or re produced sounds.

I, also, so relate means, that is, the-torsiona'l axis of in ration or the longitudinal axis between the point of support and the translating device that the resonance 'uency of vibration about such axis of the umt is below the frequency range of the sounds to be recorded or reproduced.

s In'the present referred embodiment of my invention as s own and described hereinafter, the translating device itself is closely at to the moment of inertia of the unit'about the axis of the 'sus nsion or from vibrational forces which ma be present in the supporting means and w ich rpointe out in'the appended claims.

In the draw' I s, Fig. 1 is a full-size plan view of a recor 'ng and reproducing unit, including an electric translatin device" and suitable suspension means there or, embodying my invention and applied to a phonograph apparatus adapted to use disk records; Fig. 2 is a similar view of =.the opposite or lower side of a portion of the suspension means shown in ig. 1; Fig. 3 is a view in cross section taken on line 3-3 of Fig. 1; Fig. 4 is a view in perspective of adetail of thesuspension means s ing figures; Fi 5 isa front end viewof the ortion of t e suspension means .shown in ig. 2; and Fi 6, 7, 8 and 9 are cross sectional views ta en respectively on lines 6- -6, 7-7, 8-8 and 9--9 of Fig. 3. All of the figures of. the drawings are drawn to the same scale and like parts, throughout bear the same reference numerals.

Referrin cordin an reproduci examp e includes as its t ree major portions, a translating device 10, a suspension arm 11 for the trans'latin device, and a supporting pedestal 12 for t e suspension arm. The

ranslating device is provided with a stylus.

13 which is adapted to-en'gage'a sound track or record groove .14 of spiral form provided in a surface of a' suitable record disk 15. The

record disk is carried on a suitable rotary V turntable 16-, forming part of the apparatus associated with the recording and reproducing unit, disposed in a cabinet or enclosing structure indicated by a mounting or motor board 17, on which also the supporting pedes'tal12 is provided with a fixe ivot mounting in the form of a base plate 1 secured to the motor board.

In the present example, the translating device is of the electric pickup type having, as indicated in Fig. 3,- an armature 19 pivot-' ally mountedv with the stylus 13 to vibrate therewith under the action of the sound track,

and an electric pickup coil 20 surrounding. the armature forreceiving from or trans mitting to the armature and the stylus,

pulses incident to the recording or reproduction action of the device. The pickup coil isprovided with 'suitable leads 21 carried through the. suspension arm and terminals 22 for connection with apparatus (not shown).

e reproducing unit is removable from v v is connected therewith by asuitable neck or projection 23' inserted into-one end f the arm; A suitable 3.

the'suspension arm and own in the preced- I to the drawings,'the sound reunitof the present 9? releasable terminal connection indicated at 24 is provided for the leads 21.

The suspension arm is of such length that the translating device 10 may move over the record surface about a fixed point of support provided by the pedestal 12, ina plane parallel to the record surface and also may move in a direction generally perpendicular thereto, whereby the translating stylus 13 may follow the spiral sound track and the translating device may move vertically in response to changes in the level of the record surface. To provide this arrangement, the suspension arm is pivotally connected with the supporting pedestal by a fulcrum or pivot pin 25 roviding a horizontal pivot axis exten ing through the pedestal and the arm at a point adjacent the end of the suspension arm opposite to the end to which the trans ating device is connected. The supporting pedestal is provided with a vertical pivot pm 26 which is journalled in a suitable bearing 27 provided in the base plate 18. It will be noted that the pivot pin is hollow whereby the leads 21 may be extended therethrough to a point below the supporting structure or motor board 17. By the arrangement shown, the leads are elfectively concealed throughout their length.

The suspension arm is provided with a suitable counterweight 28, on the opposite side of the pivot pin or fulcrum 25 from the translating device, of such mass or weight that it reduces the pressure of the stylus, caused by the weight of'the transating device and the suspension arm, to a desired value such that the stylus is permitted accurately to follow I the record groove without injury thereto.

Referring particularly to Figs. 1 and 3, it will be seen that lateral vibration of the stylus 13 and a lateral vibration of the motor board 17 may operate to impart to the translating device 10 a corresponding vibratory motion, since both the stylus and the connection means with the motor boardor supporting structure provide a leverage a ong a line X-X, with respect to the axis or torsional axis of the suspension arm indicated generaily by a line YY, Fig. 3. This axis is that indicated in Fig. 1 by the dotand-dash line on which the section of Fig. 3 is taken, being the central axis of the recording and reproducing unit. This axis extends longitudinally of the suspension arm and may be considered as the torsional axis of vibration of the unit.

In the usual apparatus of this character the suspension arm is rigidly mounted and is not provided with means for preventing torsional vibratory forces from being transmitted or imparted to the translating device along or about the above axis. In accordance with my invention, however, I provide not only flexibility in the suspension arm orsuspen'sion means between the translating device and its pivotal point of support in the suspension arm, but also mechanical impedance means adjacent the translating device which cooperate to prevent torsional vibrationof the translating device from either of the sources above mentioned.

Resonance vibrations are almost always possible where a mass, having a high moment of inertia about an axis of vibration, is rigidly mounted at one point. In torsional resonance, the moment of inertia is due to the mass of the translating device, taken about. an axis substantially determined by the center of mass of the translating device, and the pivotal mounting of. the suspension means therefor. This is for the reason that the angle of the stylus, as indicated in Fig. 3, and the action of the-soundtrack tend to impart a rotary or, torsional movement to the device and the suspension means along said axis,

which substantially is that of the sus ension means. The rigidity, in such cases, 0 ten lies in the stylus mounting and in the suspension means.

I have found that the objectionable torsional resonance resulting from the combination of moment of inertia and rigidity or stiflness, as set forth abovemay be overcome by reducing the natural frequency of the unit about the axis of torsional resonance to well below the lowest frequency to be reproduced.- This frequency may be changed by varying either the stiffness of the mounting at a certain point or by varying the moment of inertia about the axis of torsional resonance or vibration, or by changing both of these factors together, in proper relation to each other as in the present preferred embodiment of my invention shown and described herein. The torsional stifl'ness along the axis of the suspension means may be changed materially and the mass associated with the translating device may also be varied, the' former being preferably decreased and the latter increased as will now be explained.

In the present example, the flexibility in the mounting means between the translating device and the pivotal point of support is provided in the suspension arm itself in a region indicatedgenerally by the numeral 29 adjacent the pivotal point of support and between it and the translating device. The impedance or damping means is provided by increasing the mass of the supporting means adjacent the translating device.- The in-. crease of mass is provided, preferably, in the manner indicated in the drawings, by a pair ofspaced weights 30 30 of equal mass located at equal distances'from the torsional axis ofyibration of the unit or, in the present example, of the suspension arm.

The weights providing the increased stabilizing mass, or mechanical impedance means, are relatively Widely separated, sub-- stantially to the limits imposed by the appearance of the completed design and by a consideration of convenience of operation.

v f In accordance with well known physical laws, the amount of inertia about the torsional axis of vibration is thus increased to a desired value without materially increasing the mass attached to the translating device.

- I have found that it is preferable that the .mass included in the moment of inertia shall be a part of, integral with, or at least very rigidly secured to, the translating device itself, as in the present example. The effect of this arrangement is that the translating device is held stationary b the mass impedance, against the influence "any change of veloc-' ity of the stylus, and when forces are applied to the stylus and therefore to the sound translatin device in which it operates, the stylus is de ected or moves before the translating .-or be thrown out of the groove 'and'no re-- peating orv skipping of the sound record will occur.

It is also important that assemblage should be increased as little-as possible, in attaining the required moment of inertia and, to this end, weights are attached to the suspension arm spaced from and on opposite sides of the axis of vibration of the assembl It is obvious that in an apparatus of this character the lateral spacing of the wei hts relative to said.axis has certain limitations im sed by appearance hereinbefore mention and convenience of operation. It is also desirable, in order that t e pressure exerted by the assemblage on a record tablet shall not be increased above a desired amount, the weight or mass providing the moment of inertia be suitably counterbalanced. In the' present example, the mcreased weight imposed b the inertia or impedance means is suitab y counterbalanced Eroportion ng the countery p p y increasing its weight or weight 28, as leverage with respect to the pivot axis 25.

It is desirable to provide a constructlon "which is of pleasing appearance, adapted to P8 conceal the mertia or stabilizing mechanical impedance means and counterbalancmg weights, and to provide a flexible connection between the translating device and the pivotal point of support. To "this end the suspension arm is formed of thin-sheet material struck up alon its edges to ovide an integral marginal ange 31 whic when' in use, extends downwardly to conceal the weights, substantially as indicated m Figs. .1,

2, and 3 ofrthedrawings. The body 0 the arm is flared at its ends and is reduced between its ends to a narrow neck of U-shape the mass of the transverse section, substantially as indicated in Fig. 7 this section being taken, as indicated in ig. 3, through the region of flexibility 29. i

The flared portion of the suspension arm to which the translatin device is to be conis provided wi i a frontal opening, indicated in Fig. 5 at 32, and with a central opening 33 adapted to be closed by a suitable escutcheon plate or cover 34.

It will be seen that the suspension arm is in the form of a flanged plate ada ted to be struck up from a single piece of s set material whereby it may be manufactured at low cost and, by its form, it provides not only suitable cover means or a housing for the weights, but a thin narrow flexible section- 29 adapted to give the unit the desired flexibility tween the translating device andits pivotal point of support. Furthermore the section of the arm is adapted to fit over and conceal from view the up r end of the supporting estal 12, and to be pivotally connected t ereto by the simple pivot pin 25. The construction of the'plvot connection is shown more clearly in Fig. 8.

The counterbalance weight 28 is secured to the armor within the arm by a. single rivet 35. However, in order more accurately to locate the inertia or impedance .weights 30-30, the latter are mounted in a win shaped frame or yoke 36 in the wings or en s of which are. secured the weights 30. The yoke 36 is used-also to gain rigidity in attaching the weights 3030 to the translat ing device. As indicated in Fig. 2, the wings of the frame are adapted to lie in the frontal and more widely flared portion of the arm, and are secured thereto by any suitable means such as by mounting tabs 37, 38 spot-welded as indicated at 39, Fig. 2, to the interior of the arm. The frame is provided with a central opening 40 through which the connection for leads 21 is taken and is further provided with a tab 41 which provides a connection with the translating devicaand cooperates with the arm to provide onesurface of thefrontal opening 32 for the mounting neck of the translating device, the tab 41 being arranged to hem s aced relation to and opposite the upper sur, ace of the susnsion arm at the opening 32 whereby the neck of the translating device is received be-,

tween said tab and'said surfaces in the opening. A boltor other suitable fastening means 42 may then be passed through 'ali ned openings 43 in the neck and'in' the ta and suspension arm for secu'ring the translatingfdevice to the arm. It will be seen thatv cured to the arm at three s aced ints rovided by the tabs 37 and 38, it provides arrigid bracing means for the arm and a connection between the impedance or inertia weights '30 and the translating device. It

with the frame. as s thus becomes a unitary part of the arm itself; The frame serves not only as a mounting means for the inertia weights but also as a template for permitting the accurate location of the weights with respect to the torsional axis of vibration of the arm.

By forming the translating unit assemblage as described above, a suitable moment of inertia is provided about the axis of torsional vibration of the arm without materially increasing the weight thereof. By narrowing the construction of the suspension arm in the re ion 29 of the pivotal connection at 25 wit the pedestal 12, between the translatin device and the pivotal connection, the e ect of any stiffness of this connection, on the tendency of the suspension arm to vibrate, is materially diminished as compared with that of similar apparatus of known construction.

In my improved device or unit, the connection between the suspension arm and its supportin pedestal may also be made with less attention to machining and fitting of the parts than has been heretofore possible. A

loose pivot connection at 25 may be employed without adversely influencing the effectiveness of the unit. In fact, a loose connection has certain advantages over a more exact con-- struction as aiding the flexibility. It will therefore be seen that the present device may. be manufactured with the exercise of only ordinary mechanical skill, thereby reducing the cost of production.

I claim s my invention:

1. In a sound recording and reproducing apparatus, a translating device, a suspension means therefor having a point of support in spaced relation to sald device, a connection in said suspension means flexible about an axis extending through said device and said point of support and between said device and said support, and means connected with said device and located more adjacent thereto than said point of support providing a relatively high moment of inertia about said axis.

2. In a sound recording and reproducing apparatus, a translating device, suspension means therefor having a point of support in spaced relation to said device, a connection in said suspension means flexible about an axis extending between said point of support and the translating device, and inertia means carried by said suspension means and connected with said device adjacent thereto, said means having a moment such that it reduces the natural frequency of vibration of said device and suspension means about said axis below the frequency range of the sound energy to be translated by said device.

3. In a sound recordin and reproducing apparatus, the combination with a sound translating device having a vibratory element, 'and an apparatus supporting means, of a flexible suspension arm for said device mounted onsaid supporting means, an inertia means connected with said device and having a moment such that the arm and said device are caused to be out of resonance with vibrational forces about the axis of the arm imparted to said device from said element and from vibrational forces existing in said supporting means.

4. A sound recording and reproducing unit, including in combination, a translating device, means adapted to provide a pivotal support therefor, means providing a connec-' tion between said supporting means and said device, said connection being flexible about a torsional axis of vibration extending through said device and said supporting means, and a mechanical impedance means connected with said device adjacent thereto, said last named means having a relatively low mass and high inertia about said torsional axis of vibration.

5. A sound recording and reproducing unit including a translatin device and support therefor, characterize by the fact that a mass having relatively high moment of inertia about an axis extending through said unit and the support is embodied in the unit adjacent to the translating device in direct connection therewith, and that a region of flexibility is provided about said axis between the translating device and the support.

6. The combination with a sound translating device having a movable stylus and a torsional axis of vibration about which movement of the stylus tends to set up movement of the translating device, of means directly connected with and located adjacent to the translating device, providing a relatively high moment of inertia about said axis, and means flexible about said axis providing a support for said device and first named means.

7. In sound reproducing apparatus and the like,the combination with a sound translating device, of a supporting means for said device providing a flexible mounting for said device in said apparatus, and inertia means directly connected with and located adjacent to said device, providing relatively high mechanical impedance to vibrational movement of said device.

8. The'combination with a sound translating device having a movable stylus, and a torsional axis of-vibration about which vibrational movement of the stylus tends to set up a corresponding movement of the translating device, of means directly connected with and located adjacent to the translating device providing a relatively high moment of inertia about said axis, a support for said device in spaced relation thereto, and means providing a region of flexibility about said axis between said translating device and said support.

9. In a sound recording and reproducing unit, a support, a translating device, an arm i A tivel of vi ration of the translating device, and beconnected at one end with said device and pivotally connected adj acentits opposite end with the support, and inertia means associated d1- rectl with said device having a mass equally I distributed on opposite sides of a longitudinal axis of the unit, which axis extends through the translatin device and the pivotal connection with e su port, and said arm having a region of flexibility about said axis be- 1 tween said inertia means andtsaid support.

10. In a sound recording and reproducing unit, a support, a translating device, an arm rigidly connected at one end with said device and pivotally connected adjacent its opposite end with the sup ort, and inertia means hava mass equal distributed on opposite s iifes of a longitu inal axis of the unit extending through the translating device and the pivotal connectionwith the support, said arm having marginal flanges providing a channel oi U-shaped transverse section between its ends, and said channel being reduced in transverse section to provide a region vof flexibility aboutsaid axis between said translating device and inertia means and said pivotal connection.

11. In a sound recordin and reproducing unit, a support, a translating device, an arm rigidly connected at one end with said device and pivotallyconnected ad'acent its opposite end with the su port, a yo e rigidly secured to the translating device transversely of a lon 'tudinal axisof the unit, spaced weights of equal mass carried by the yo e on opposite sides of said axis in equal spaced re ation thereto, said arm havin marginal flanges providing a channel of -shaped transverse section between said ends, and said channel.

being reduced in transverse sectionto provide a re 'on of flexibility about said axis between sai translating device and weights and said pivotal connection with the support. A

12. The combination with a sound translating device havin a body portion and an operating element re ativelv movable with respect thereto for thetranslation of sound energy, of

'a suspension means for said device, a support for said suspension means, and means for preventing distortion in the translation of sound 9 energy by undesired relative movement between said body and element, said means in- 1 of inertia of the pickup device a end'of which the pickupdevice is aflixed,

ing rigidly connected directly with said device, and supportin means for said translating device arrang to provide a flexible connection between said translating device and said su porti structure;

14. he com ination with a sound translating device havin a movable stylus, and

supportin means t erefor, said translating device an the supporting means being arranged in spacedv relation to each other, of means for preventing vibratory movement of said translating device about an axis extending through said device and said supporting means in response to vibratory forces generated by movement of said stylus and vibratory forces transmitted through said supporting means, said vibration preventin means including a mass havingra relative y hi h moment of inertia about said axis and re atively low intrinsic wei ht, and a connection providing a region of exibilit about said axis between said device and sai supporting means. N

15. A sound recordin and reproducing unit including a translatin device and support therefor, characterize by the fact that a mass having relatively high moment'of in-' ertia about an axisextendin through said unit and thesupport is em adjacent to the translatin device in direct connection therewith an that supporting means for the transiating device and said mass having a region of flexibility located in spaced relation tosaid device and said mass is Iprovided in said unit.

16. T up device and a suspension arm therefor having with said device a common torsional axis of vibration extending along the arm, of

means having a rigid connection with the pickup device for efiectively increasing the amount of inertiaof said device about said e combination with an electric pickied in the unit I torsional axis of vibration, and said arm r0 viding a region of torsional flexibility a at said axis.

17. 'ihe combination with an electric pickup device having an axis about which it tends to move in response to vibrational forces, of

means for efiectively increasin the moment at said axisi supportin means for said device connecte therewith in spaced relation thereto, and sus- I pension means for said device providing said connection and a region of torsional flexibility about said axis intermediate of the inertia increasiiigmeans and. the supporting means.

18. In combination, an electric pickup device, a pivoted supporting arm' to the free and means carried by the arm for effectively increasing the moment of inertia of the 'pickflexibility intermediate of 'the inertia increasing means and the pivoted end thereof.

19. In an electric sound recording and reproducing apparatus, the combination of a motorboard, a pickup suspension arm, a supporting pedestal therefor mounted. on the motorboard, an electric (pickup device having a body mounted on sai arm and a movable stylus in said body, means carried by the arm for eflectively increasing the moment of inertia of the pickup device about a torsional axis of vibration extending along the arm and said arm having a region of torsional exibility between said inertia increasing means and the supporting pedestal.

'20. In an electric sound recordin and reproducing apparatus, the combination of a motorboard a pickup suspension arm, a supporting pedestal therefor mounted on the .motorboard, an electric pickup device having a body mounted on said arm and a movable st lus in said body, and means for preventing vi ratory movement of the body of the pickand said arm providing a region of torsional flexibility along its length and about said axis between said device and the supporting ped'.

estal.

In testimony whereof, I have hereunto sub-. scribed my name this. 9th day of March 1931. JAMES M. KENDALL.

device in response to vibratory movement 

